Parents who blame themselves for children who are unambitious, irresponsible, moody or suicidal may be full of unwarranted self-reproach, Cohen contends, because the influence of parenting on a child's personality development is much weaker than most people assume. According to this professor of psychology at the University of Texas at Austin, genetic factors play a pervasive role in molding individual capabilities, dispositions, habits, intelligence and emotional adjustment. He bases this conclusion in part on studies demonstrating the close psychological resemblance of identical twins reared apart, on studies of adoptees and on recent investigations pointing to startling connections between DNA patterns or single genes and personality traits. This highly accessible, forcefully argued report is a brilliant synthesis of the new genetic findings and their often stunning implications, though Cohen overstates his case, citing, for example, debatable studies that conclude that attitudes about the death penalty, religion, patriotism and sex before marriage have a high degree of heritability. Far from endorsing genetic determinism, however, Cohen underscores the importance of parenting in fostering security, learning, civility and self-confidence. Further, he believes that individual autonomy and unforeseeable life circumstances make it hard to predict how a child grows into adulthood. His ""seven rules of parenting"" combine good common sense with some cautions, as when he asserts, ""Parents have limited moral responsibility for how a child turns out."" This opinionated salvo in the nature vs. nurture debate will challenge general readers, psychologists, scientists and thoughtful parents. (Apr.)